The present invention relates generally to an apparatus for aircraft flight management, and particularly to an apparatus for intervisibility calculation with respect to digital terrain elevation data (DTED).
Digital terrain elevation data represents surface elevation at discrete "data posts." Each data post has a surface location or address, e.g., latitude and longitude, and an associated altitude, i.e., relative to sea level. Thus, a simple form of a DTED database would deliver a scaler altitude in response to longitude and latitude input. More complicated DTED databases have been developed for certain applications. For example, U.S. Pat. No. 4,899,292 issued Feb. 6, 1990 to J. F. Dawson and E. W. Ronish shows a tessellation method for creating a spherical database by warping a digital map, including digital terrain elevation data, by longitude and latitude parameters.
DTED database systems are used in flight mission computer systems and flight planning strategy in military applications to aid in, for example, covert and evasive flight operations. As used in mission computer systems, a DTED database can aid a pilot in time-critical maneuvers such as terrain following flight or in selecting evasive routes having low observability with respect to a given threat position. Such threat positions may be known in advance and included in the DTED database, or detected while in flight. The computation speed required in accessing and calculating routes or alternatives based on DTED systems can be vitally critical, especially for computations executed repeatedly to keep a pilot fully appraised of current terrain conditions and route alternatives. Thus, improvements in methods of accessing DTED and computations based on extracted DTED are not simply improvements in computational elegance, but can be life-saving and critical to mission success.